Integrated circuits are continuing to be scaled to smaller dimensions by semiconductor device manufacturers. Interconnect process development, specifically inlaid interconnect technology, is an area being investigated in an effort to continue reducing circuit dimensions. However, the reduction in the size of the interconnects results in a corresponding increase in circuit current density and presents problems with respect to electromigration. This can result in an irreversible change in the resistance and reliability of the circuit over time.
Copper is currently being investigated as an alternative to aluminum to overcome problems introduced as a result of increasing current density. Copper offers intrinsic advantages over aluminum, including its lower resistivity and improved electromigration resistance. However, the use of copper as an alternative in advanced interconnect technologies does not totally eliminate the problems of electromigration. As interconnect dimensions continue to shrink, electromigration will continue to be a reliability concern.
In addition, using copper for forming interconnects introduces new problems with respect to reliability. Copper adheres poorly to oxide-containing films and passivating polymers, such as polyimide. This is not only a concern during the formation of vias and interconnects, but also when assembling and packaging completed semiconductor devices. Reliability problems have been reported with respect to adhesion when using essentially pure copper films to form bond pads. Among them include a failure resulting from poor adhesion between the copper bond pad and portions of the passivation film overlying the copper bond pad.